1. Technical Field
The present invention relates to a combustion apparatus comprising a plurality of longitudinally (in the back-and-forth direction) elongated gas burners, each of the gas burners having an air-fuel mixing tube portion, and a burner port on an upper end of the gas burner for ejecting air-fuel mixture from the air-fuel mixing tube portion.
2. Background Art
This kind of combustion apparatus is provided with a plurality of gas nozzles each lying opposite to a gas inlet port which is on an upstream end of the air-fuel mixing tube portion of each of gas burners, and a damper to cover the plurality of gas inlet ports of the plurality of gas burners. The damper has formed therein ventilation holes which overlap the gas inlet ports of the plurality of gas burners. Conventionally, there is known an arrangement in which each of the ventilation holes is provided with obstacles to which fuel gas to be ejected from the gas nozzles strike so as to accelerate the mixing between the fuel gas and primary air (see, for example, JP 2004-60897 A).
According to this known art, thanks to the acceleration of mixing between the fuel gas and the primary air, the distribution (air-fuel ratio distribution), in the longitudinal direction, of the air-fuel ratio of the air-fuel mixture to be ejected from the burner ports can be made uniform in all of the gas burners. However, the frequencies of the combustion vibrations to be generated in longitudinally several positions of each gas burner coincide with the frequencies of the combustion vibrations to be generated in longitudinally the same positions of the other gas burners, thereby increasing the combustion noises.
Further, conventionally there is known an arrangement in which the area of the openings of the ventilation holes to be formed in the damper are made larger in part of the gas burners than in the remaining gas burners (see, for example, JP 1998-288315 A). According to the disclosure therein, there will give rise to a difference, due to the difference in the air-fuel ratio of the air-fuel mixture, between the frequencies of the combustion vibrations in some of the gas burners and the frequencies of the combustion vibrations in the other gas burners. As a result of interference actions due to the difference in frequencies, the combustion noises can be suppressed. However, if the air-fuel ratio of the air-fuel mixture is varied to the air-rich side by enlarging the area of openings of the ventilation holes, flame lifting is likely to occur at the time of high intensity combustion.